ADU rules by state and city
Start with your state: state law decides what every city must allow. Then check your city for its size limits, fees, permit steps and who to call.
Arizona
What Arizona state law lets you build: two ADUs per single-family lot in larger cities and all counties, size limits, 5-foot setbacks, no parking.
California
California's statewide ADU and junior ADU rules for 2026: sizes, height, setbacks, parking, fees, owner occupancy, the 60-day deadline, SB 9 and HCD.
Colorado
What Colorado's 2024 ADU law (HB24-1152) lets you build, which cities it covers, and the limits on size, setbacks, parking, owner rules and HOAs.
Massachusetts
What the 2024 Affordable Homes Act lets you build: one ADU by right in single-family zones, up to 900 sq ft, no owner-occupancy rule, limited parking.
Montana
What Montana law lets you build: one ADU by right in cities, county ADUs from 2025, duplexes in cities of 5,000+, parking limits and the court rulings.
Oregon
Oregon's ADU and middle housing laws explained: where ADUs are allowed, parking and owner-occupancy bans, rural ADUs, HOA rules and where to complain.
Texas
Texas has no statewide ADU law in 2026. What the 2025 bills did (SB 15 small lots, HB 24 zoning protests), what failed (SB 673) and who sets ADU rules.
Washington
Washington's ADU and middle housing laws explained: two ADUs per lot, size, height, parking, fees, owner occupancy and when cities must comply.
We add states and cities as we check them against official sources. Not listed yet? Your city's planning or building department is the place to ask, and the general permit steps apply almost everywhere.